linux-kernel - [PATCH] drm: rcar-du: do not restart rcar-du groups on gen3

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Date:   Tue, 23 Nov 2021 16:20:11 +0100
From:   Michael Rodin <mrodin@...adit-jv.com>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Kieran Bingham <kieran.bingham+renesas@...asonboard.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        <dri-devel@...ts.freedesktop.org>,
        <linux-renesas-soc@...r.kernel.org>, <linux-kernel@...r.kernel.org>
CC:     Michael Rodin <mrodin@...adit-jv.com>, <michael@...in.online>,
        <efriedrich@...adit-jv.com>, <erosca@...adit-jv.com>
Subject: [PATCH] drm: rcar-du: do not restart rcar-du groups on gen3

Restarting a display unit group can cause a visible flicker on the display.
Particularly when a LVDS display is connected to a Salvator board and an
HDMI display is (re)connected, then there will be 2 visible flickers on the
LVDS display:

 1. during atomic_flush (The need_restart flag is set in this case by
    rcar_du_vsp_enable.):
  rcar_du_crtc_atomic_flush
    rcar_du_crtc_update_planes
      ...
      ...
      /* Restart the group if plane sources have changed. */
      if (rcrtc->group->need_restart)
              rcar_du_group_restart(rcrtc->group);
 2. during atomic_enable:
  rcar_du_crtc_atomic_enable
    rcar_du_crtc_start
      rcar_du_group_start_stop(rcrtc->group, true);

To avoid flickers in all use cases, do not restart DU groups on the Gen3
SoCs at all, since it is not required any more.

Signed-off-by: Michael Rodin <mrodin@...adit-jv.com>
---
 drivers/gpu/drm/rcar-du/rcar_du_group.c | 5 ++++-
 drivers/gpu/drm/rcar-du/rcar_du_vsp.c   | 2 --
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/rcar-du/rcar_du_group.c b/drivers/gpu/drm/rcar-du/rcar_du_group.c
index 8665a1d..ff0a1c8 100644
--- a/drivers/gpu/drm/rcar-du/rcar_du_group.c
+++ b/drivers/gpu/drm/rcar-du/rcar_du_group.c
@@ -250,7 +250,7 @@ void rcar_du_group_start_stop(struct rcar_du_group *rgrp, bool start)
 	 * when the display controller will have to be restarted.
 	 */
 	if (start) {
-		if (rgrp->used_crtcs++ != 0)
+		if (rgrp->used_crtcs++ != 0 && rgrp->dev->info->gen != 3)
 			__rcar_du_group_start_stop(rgrp, false);
 		__rcar_du_group_start_stop(rgrp, true);
 	} else {
@@ -263,6 +263,9 @@ void rcar_du_group_restart(struct rcar_du_group *rgrp)
 {
 	rgrp->need_restart = false;
 
+	if (rgrp->dev->info->gen == 3)
+		return;
+
 	__rcar_du_group_start_stop(rgrp, false);
 	__rcar_du_group_start_stop(rgrp, true);
 }
diff --git a/drivers/gpu/drm/rcar-du/rcar_du_vsp.c b/drivers/gpu/drm/rcar-du/rcar_du_vsp.c
index b7fc5b0..a652c06 100644
--- a/drivers/gpu/drm/rcar-du/rcar_du_vsp.c
+++ b/drivers/gpu/drm/rcar-du/rcar_du_vsp.c
@@ -88,8 +88,6 @@ void rcar_du_vsp_enable(struct rcar_du_crtc *crtc)
 	 * Ensure that the plane source configuration takes effect by requesting
 	 * a restart of the group. See rcar_du_plane_atomic_update() for a more
 	 * detailed explanation.
-	 *
-	 * TODO: Check whether this is still needed on Gen3.
 	 */
 	crtc->group->need_restart = true;
 
-- 
2.7.4